The present invention enables the molecular manufacturing of atomically precise diamond and diamondoid materials with fully deterministic atomic placement control. Diamondoid mechanosynthesis is the first known method to enable the fabrication of atomically precise diamond or diamondoid structures. No previously existing method for synthesizing diamond allows atomically precise diamond structures to be fabricated to atomic specifications with single-atom feature sizes.
Conventional Diamond Manufacturing. Conventional diamond manufacturing methods are bulk processes in which the diamond crystal structure is manufactured by statistical processes lacking positional control. In such processes, new atoms of carbon arrive at the growing diamond crystal structure having random positions, energies, and timing. Growth extends outward from initial nucleation centers having uncontrolled size, shape, orientation and location, yielding an inferior product having irregular atomic-scale features.
Existing bulk processes can be divided into three principal methods—(1) high pressure, (2) low pressure hydrogenic, and (3) low pressure nonhydrogenic.
(1) In the high pressure bulk method of producing diamond artificially, powders of graphite, diamond, or other carbon-containing substances are subjected to high temperature and high pressure to form crystalline diamond. High pressure processes are of several types:
(A) Impact Process. The starting powder is instantaneously brought under high pressure by applying impact generated by, for example, the explosion of explosives and the collision of a body accelerated to a high speed. This produces granular diamond by directly converting the starting powder material having a graphite structure into a powder composed of grains having a diamond structure. This process has the advantage that no press as is required, as in the two other processes, but there is difficulty in controlling the size of the resulting diamond products. Nongraphite organic compounds can also be shock-compressed to produce diamond.
(B) Direct Conversion Process. The starting powder is held under a high static pressure of 13-16 GPa and a high temperature of 3,000-4,000° C. in a sealed high pressure vessel. This establishes stability conditions for diamond, so the powder material undergoes direct phase transition from graphite into diamond, through graphite decomposition and structural reorganization into diamond. In both direct conversion and flux processes, a press is widely used and enables single crystal diamonds to be grown as large as several millimeters in size.
(C) Flux Process. As in direct conversion, a static pressure and high temperature are applied to the starting material, but here fluxes such as Ni and Fe are added to allow the reaction to occur under lower pressure and temperature conditions, accelerating the atomic rearrangement which occurs during the conversion process. For example, high-purity graphite powder is heated to 1500-2000° C. under 4-6 GPa of pressure in the presence of iron catalyst, and under this extreme, but equilibrium, condition of pressure and temperature, graphite is converted to diamond: The flux becomes a saturated solution of solvated graphite, and because the pressure inside the high pressure vessel is maintained in the stability range for diamond, the solubility for graphite far exceeds that for diamond, leading to diamond precipitation and dissolution of graphite into the flux. Every year about 75 tons of diamond are produced industrially this way.
(2) In the low pressure hydrogenic bulk method of producing diamond artificially, widely known as CVD or Chemical Vapor Deposition, hydrogen (H2) gas mixed with a few percent of methane (CH4) is passed over a hot filament or through a microwave discharge, dissociating the methane molecule to form the methyl radical (CH3) and dissociating the hydrogen molecule into atomic hydrogens (H). Acetylene (C2H2) can also be used in a similar manner as a carbon source in CVD. Diamond or diamond-like carbon films can be grown by CVD epitaxially on diamond nuclei, but such films invariably contain small contaminating amounts (0.1-1%) of hydrogen which gives rise to a variety of structural, electronic and chemical defects relative to pure bulk diamond. Hydrogen is generally regarded as an essential part of the reaction steps in forming diamond film during CVD, and atomic hydrogen must be present during low pressure diamond growth to: (1) stabilize the diamond surface, (2) reduce the size of the critical nucleus, (3) “dissolve” the carbon in the feedstock gas, (4) produce carbon solubility minimum, (5) generate condensable carbon radicals in the feedstock gas, (6) abstract hydrogen from hydrocarbons attached to the surface, (7) produce vacant surface sites, (8) etch (regasify) graphite, hence suppressing unwanted graphite formation, and (9) terminate carbon dangling bonds. Both diamond and graphite are etched by atomic hydrogen, but for diamond, the deposition rate exceeds the etch rate during CVD, leading to diamond (tetrahedral sp3 bonding) growth and the suppression of graphite (planar sp2 bonding) formation. (Most potential atomic hydrogen substitutes such as atomic halogens etch graphite at much higher rates than atomic hydrogen.) Currently, diamond synthesis from CVD is routinely achieved by more than 10 different methods. Low pressure or CVD hydrogenic metastable diamond growth processes are of several types:
(A) Hot Filament Chemical Vapor Deposition (HFCVD). Filament deposition involves the use of a dilute (0.1-2.5%) mixture of hydrocarbon gas (typically methane) and hydrogen gas (H2) at 50-1000 torr which is introduced via a quartz tube located just above a hot tungsten filament or foil which is electrically heated to a temperature ranging from 1750-2800° C. The gas mixture dissociates at the filament surface, yielding dissociation products consisting mainly of radicals including CH3, CH2, C2H, and CH, acetylene, and atomic hydrogen, as well as unreacted CH4 and H2. A heated deposition substrate placed just below the hot tungsten filament is held in a resistance heated boat (often molybdenum) and maintained at a temperature of 500-1100° C., whereupon diamonds are condensed onto the heated substrate. Filaments of W, Ta, and Mo have been used to produce diamond. The filament is typically placed within 1 cm of the substrate surface to minimize thermalization and radical recombination, but radiation heating can produce excessive substrate temperatures leading to nonuniformity and even graphitic deposits. Withdrawing the filament slightly and biasing it negatively to pass an electron current to the substrate assists in preventing excessive radiation heating.
(B) High Frequency Plasma-Assisted Chemical Vapor Deposition (PACVD). Plasma deposition involves the addition of a plasma discharge to the foregoing filament process. The plasma discharge increases the nucleation density and growth rate, and is believed to enhance diamond film formation as opposed to discrete diamond particles. There are three basic plasma systems in common use: a microwave plasma system, a radio frequency or RF (inductively or capacitively coupled) plasma system, and a direct current or DC plasma system. The RF and microwave plasma systems use relatively complex and expensive equipment which usually requires complex tuning or matching networks to electrically couple electrical energy to the generated plasma. The diamond growth rate offered by these two systems can be quite modest, on the order of ˜1 micron/hour. Diamonds can also be grown in microwave discharges in a magnetic field, under conditions where electron cyclotron resonance is considerably modified by collisions. These “magneto-microwave” plasmas can have significantly higher densities and electron energies than isotropic plasmas and can be used to deposit diamond over large areas.
(C) Oxyacetylene Flame-Assisted Chemical Vapor Deposition. Flame deposition of diamond occurs via direct deposit from acetylene as a hydrocarbon-rich oxyacetylene flame. In this technique, conducted at atmospheric pressure, a specific part of the flame (in which both atomic hydrogen (H) and carbon dimers (C2) are present) is played on a substrate on which diamond grows at rates as high as >100 microns/hour.
(3) In the low pressure nonhydrogenic bulk method of producing diamond artificially, a nonhydrogenic fullerene (e.g., C60) vapor suspended in a noble gas stream or a vapor of mixed fullerenes (e.g., C60, C70) is passed into a microwave chamber, forming a plasma in the chamber and breaking down the fullerenes into smaller fragments including isolated carbon dimer radicals (C2). (Often a small amount of H2, e.g., ˜1%, is added to the feedstock gas.) These fragments deposit onto a single-crystal silicon wafer substrate, forming a thickness of good-quality smooth nanocrystalline diamond (15 nm average grain size, range 10-30 nm crystallites) or ultrananocrystalline diamond (UNCD) diamond films with intergranular boundaries free from graphitic contamination, even when examined by high resolution TEM at atomic resolution. Fullerenes are allotropes of carbon, containing no hydrogen, so diamonds produced from fullerene precursors are hydrogen-defect free—indeed, the Ar/C60 film is close in both smoothness and hardness to a cleaved single crystal diamond sample. The growth rate of diamond film is ˜1.2 microns/hour, comparable to the deposition rate observed using 1% methane in hydrogen under similar system deposition conditions. Diamond films can, using this process, be grown at relatively low temperatures (<500° C.) as opposed to conventional diamond growth processes which require substrate temperatures of 800-1000° C.
Ab initio calculations indicate that C2 insertion into carbon-hydrogen bonds is energetically favorable with small activation barriers, and that C2 insertion into carbon-carbon bonds is also energetically favorable with low activation barriers. A mechanism for growth on the diamond C(100) (2×1):H reconstructed surface with C2 has been proposed. A C2 molecule impinges on the surface and inserts into a surface carbon-carbon dimer bond, after which the C2 then inserts into an adjacent carbon-carbon bond to form a new surface carbon dimer. By the same process, a second C2 molecule forms a new surface dimer on an adjacent row. Then a third C2 molecule inserts into the trough between the two new surface dimers, so that the three C2 molecules incorporated into the diamond surface form a new surface dimer row running perpendicular to the previous dimer row. This C2 growth mechanism requires no hydrogen abstraction reactions from the surface and in principle should proceed in the absence of gas phase atomic hydrogen.
The UNCD films were grown on silicon (Si) substrates polished with 100 nm diamond grit particles to enhance nucleation. Deposition of UNCD on a sacrificial release layer of SiO2 substrate is very difficult because the nucleation density is 6 orders of magnitude smaller on SiO2 than on Si. However, the carbon dimer growth species in the UNCD process can insert directly into either the Si or SiO2 surface, and the lack of atomic hydrogen in the UNCD fabrication process permits both a higher nucleation density and a higher renucleation rate than the conventional H2/CH4 plasma chemistry, so it is therefore possible to grow UNCD directly on SiO2.
Besides fullerenes, it has been proposed that polymantanes, small hydrocarbons made of one or more fused cages of adamantane (C10H16, the smallest unit cage of hydrogen-terminated crystalline diamond) could be used as the carbon source in nonhydrogenic diamond CVD. It is suggested in U.S. Pat. No. 6,783,589 that the injection of polymantanes could facilitate growth of CVD-grown diamond film by allowing carbon atoms to be deposited at a rate of about 10-100 or more at a time, unlike conventional plasma CVD in which carbons are added to the growing film one atom at a time, possibly increasing diamond growth rates by an order of magnitude or better. Atomistic simulations to study thin-film growth via the deposition of very hot (119-204 eV/molecule; 13-17 km/sec) beams of adamantane molecules on hydrogen-terminated diamond C(111) surfaces, with forces on the atoms in the simulations calculated using a many-body reactive empirical potential for hydrocarbons, found that during the deposition process the adamantane molecules react with one another and the surface to form hydrocarbon thin films that are primarily polymeric with the amount of adhesion depending strongly on incident energy. Despite the fact that the carbon atoms in the adamantane molecules are fully sp3 hybridized, the films contain primarily sp2 hybridized carbon with the percentage of sp2 hybridization increasing as the incident velocity goes up. However, cooler beams might allow more consistent sp3 diamond deposition, and other techniques have deposited diamond-like carbon (DLC) films with a higher percentage of sp3 hybridization from adamantane.
Positional Diamond Manufacturing via Mechanosynthesis. The positional assembly of diamondoid structures, some almost atom by atom, using molecular feedstock has been examined theoretically via computational models of diamondoid mechanosynthesis by Jingping Peng, Robert A. Freitas Jr., Ralph C. Merkle, James R. Von Ehr, John N. Randall, George D. Skidmore, “Theoretical Analysis of Diamond Mechanosynthesis. Part III. Positional C2 Deposition on Diamond C(110) Surface using Si/Ge/Sn-based Dimer Placement Tools,” J. Comput. Theor. Nanosci. 3(February 2006):28-41; Berhane Temelso, C. David Sherrill, Ralph C. Merkle, Robert A. Freitas Jr., “High-level Ab Initio Studies of Hydrogen Abstraction from Prototype Hydrocarbon Systems,” J. Phys. Chem. A 110 (28 Sep. 2006):11160-11173; Berhane Temelso, C. David Sherrill, Ralph C. Merkle, Robert A. Freitas Jr., “Ab Initio Thermochemistry of the Hydrogenation of Hydrocarbon Radicals Using Silicon, Germanium, Tin and Lead Substituted Methane and Isobutane,” J. Phys. Chem. A 111(15 Aug. 2007):8677-8688; and K. Eric Drexler, Nanosystems: Molecular Machinery, Manufacturing, and Computation, John Wiley & Sons, New York, 1992, Chapter 8. Diamondoid mechanosynthesis is the controlled addition of individual carbon atoms, carbon dimers (C2), single methyl (CH3) or like groups to the growth surface of a diamond crystal lattice workpiece in a vacuum or other inert manufacturing environment. Covalent chemical bonds are formed one by one as the result of positionally constrained mechanical forces applied at the tip of a scanning probe microscope (SPM) apparatus.
The first experimental demonstration of positional atomic assembly of any kind occurred in 1989 when Eigler and Schweizer employed an SPM to spell out the IBM logo using 35 xenon atoms arranged on nickel surface, though no covalent bonds were formed. D. M. Eigler, E. K. Schweizer, “Positioning Single Atoms with a Scanning Tunnelling Microscope,” Nature 344(5 Apr. 1990):524-526. The use of precisely applied mechanical forces to induce site-specific chemical transformations is called positional mechanosynthesis. In 2003, Oyabu et al achieved the first experimental demonstration of purely mechanical positional chemical synthesis (mechanosynthesis) on a heavy atom using only mechanical forces to make and break covalent bonds—first abstracting and then rebonding a single silicon atom to a silicon surface with SPM positional control in vacuum at low temperature using an atomically imprecise tip. Noriaki Oyabu, Oscar Custance, Insook Yi, Yasuhiro Sugawara, Seizo Morita, “Mechanical vertical manipulation of selected single atoms by soft nanoindentation using near contact atomic force microscopy,” Phys. Rev. Lett. 90(2 May 2003):176102. In 2004, Oyabu et al repeated this experimental demonstration with a single Ge atom on a Ge surface. N. Oyabu, O. Custance, M. Abe, S. Moritabe, “Mechanical Vertical Manipulation of Single Atoms on the Ge(111)-c(2×8) Surface by Noncontact Atomic Force Microscopy,” Abstracts of Seventh International Conference on non-contact Atomic Force Microscopy, Seattle, Wash., USA, 12-15 September 2004, p. 34.
The assumption of positionally controlled highly reactive tools operating in vacuum permits the use of novel and relatively simple reaction pathways. Following early general proposals in 1992 by Drexler for possible diamond mechanosynthetic tools and sketches of a few possible approaches to specific reaction pathways, in a partial set of tools and reaction pathways for diamondoid mechanosynthesis was outlined. Ralph C. Merkle, “A proposed ‘metabolism’ for a hydrocarbon assembler,” Nanotechnology 8 (1997):149-162. Merkle's “hydrocarbon metabolism” scheme, which used 9 primary tooltypes plus several intermediates (some incompletely defined), employed at least 6 different element types (C, Si, Sn, H, Ne, and one unspecified transition metal), and required another unspecified “vitamin molecule” possibly including additional element types. It did not show 100% process closure, and in most cases did not specify complete reaction sequences.
The term “mechanosynthesis” is briefly mentioned in the text of U.S. Pat. No. 6,339,227 where it is undefined, and the related U.S. Pat. No. 6,348,700, where it is described as being facilitated by voltage pulses applied through an STM tip. Each of these references suffers from the disadvantage of not describing mechanically forcing a chemical reaction to occur.
Information relevant to attempts to address mechanically forcing a chemical reaction to occur can be found in U.S. Pat. Nos. 5,372,659 and 6,017,504. However, each one of these references suffers from the disadvantage of describing mechanically-forced chemical reactions that are not positionally controlled and not atomically precise.
Information relevant to attempts to address site-specific positional control of chemical reactions can be found in U.S. Pat. Nos. 4,987,312; 5,144,148; 6,987,277; and 7,326,923. However, each of these references suffers from the disadvantage that the described chemical reactions are driven by the application of voltages, electrical fields, electrostatic forces, or tunneling currents, and are not driven purely by the application of mechanical force.
Information relevant to attempts to address site-specific positional control of chemical reactions using mechanical force can be found in U.S. Pat. Nos. 5,824,470; 6,422,077; 6,716,409; 6,864,481; 6,886,395; and 7,189,455. However, each of these references suffers from the disadvantage that they employ atomically imprecise tips or employ bulk processes to prepare such tips.
Information relevant to attempts to address site-specific positional control of chemical reactions using mechanical force applied with atomically precise tips can be found in U.S. Pat. Nos. 6,827,979; 6,835,534; 7,211,795; 7,282,710; 7,291,284; 7,326,293; and 7,381,625. However, each of these references suffers from one or more of the following disadvantages: SPM tips are applied in nanolithographic processes that are not uniformly atomically precise; coatings or related bulk processes are employed; no chemical reactions are involved; or chemical reactions yield an atomically imprecise product.
Information relevant to attempts to address applications of extracting naturally occurring polyadmanatane molecules, also referred to as diamondoids, from natural petroleum sources using bulk processes can be found in U.S. Pat. Nos. 4,952,749; 7,049,374; 7,309,476; and 7,312,562. However, each of these references suffers from the disadvantage that they do not teach that diamondoids can be manufactured using positionally controlled mechanosynthesis. Information relevant to attempts to address the use of molecular building blocks can be found in U.S. Pat. No. 6,531,107. However, this reference suffers from the disadvantages of specifying the use of large boron-based molecular building blocks, employing self-assembly rather than positional control, and yielding products that are not uniformly atomically precise.
Toolset for Diamondoid Mechanosynthesis. The minimal toolset includes nine specific tools, three of which have previously been discussed in the literature:
(A) Hydrogen Abstraction Tool. Undoped diamond normally consists of a rigid lattice of carbon atoms surface-passivated by hydrogen atoms, so a necessary aspect of diamond mechanosynthesis is the positionally-controlled abstraction (removal) of hydrogen atoms from stiff hydrocarbon structures—including hydrogens terminating the surface of the diamond crystal lattice, hydrogens present in feedstock molecules, and hydrogen atoms bonded to partly or fully completed mechanosynthetic tools or handle structures. The archetypal hydrogen abstraction tool described by Temelso et al. 2006 makes use of an ethynyl (acetylene) radical attached to a handle structure that first approaches a hydrogenated diamond surface as a site-specific active tool and then is retracted from a partially dehydrogenated diamond surface as a spent tool. The simplest practical HAbst tool is the ethynyl radical mounted on an adamantane base which is readily covalently bonded to a larger handle structure by extension of a regular diamond lattice of which the adamantane base is a unit cage. Site-specific hydrogen abstraction from crystal surfaces, though not purely mechanical abstraction, has also been achieved experimentally by abstracting an individual hydrogen atom from a specific atomic position in a covalently-bound hydrogen monolayer on a flat Si(100) surface, using an electrically-pulsed STM tip in ultrahigh vacuum. M. C. Hersam, G. C. Abeln, J. W. Lyding, “An approach for efficiently locating and electrically contacting nanostructures fabricated via UHV-STM lithography on Si(100),” Microelectronic Engineering 47(June 1999):235-237. However, this method suffers from the disadvantage that the described chemical reactions are driven by the application of voltages, electrical fields, electrostatic forces, or tunneling currents, and are not driven purely by the application of mechanical force.
(B) Hydrogen Donation Tool. Another necessary aspect of diamond mechanosynthesis is the positionally-controlled donation of hydrogen atoms to stiff hydrocarbon structures—including hydrogens terminating the surface of the diamond crystal lattice or to partly or fully completed mechanosynthetic tools or handle structures. The simplest hydrogen donation tool described by Temelso et al. 2007 is the Group IV-substituted adamantane such as the germanium-substituted adamantane that is brought up to a partially dehydrogenated diamond surface as a site-specific active tool and then is retracted from a now-rehydrogenated diamond surface as a spent tool. The Hydrogen Donation tool is readily covalently bonded to a larger handle structure by extension of a regular diamond lattice of which the adamantane base is a unit cage. Site-specific hydrogen donation to crystal surfaces, though not purely mechanical donation, has also been achieved experimentally by depositing hydrogen atoms from an STM tungsten tip to a monohydride Si(100)-H(2×1) surface by applying a +3.5V voltage bias to diffuse the hydrogens to the tungsten tip, followed by −8.5V 300 ms pulses to induce electronic excitations to break the W—H bond, in ultrahigh vacuum. D. H. Huang, Y. Yamamoto, “Physical mechanism of hydrogen deposition from a scanning tunneling microscopy tip,” Appl. Phys. A 64(April 1997):R419-R422. However, this method suffers from the disadvantage that the described chemical reactions are driven by the application of voltages, electrical fields, electrostatic forces, or tunneling currents, and are not driven purely by the application of mechanical force.
(C) Dimer Placement Tool. A principal challenge in diamond mechanosynthesis is the controlled addition of carbon atoms to the growth surface of a diamond crystal lattice. One efficient method is to add a pair of triple-bonded carbon atoms (a C2 dimer) in one operation. The function of a dimer placement tool described by Peng et al. is to position the dimer, then to bond the dimer at a precisely chosen lattice location on a growing molecular structure, and finally to withdraw the tool—leaving behind two carbon atoms bonded to the growing structure. This tool allows fabrication of diamond structures having an even number of C atoms that are geometrically accessible to the tool, given the limits imposed by tool aspect ratio. Monomer C and Ge atoms can more conveniently be transferred to diamondoid workpieces by adding .CH2 groups using the Methylene or GermylMethylene tools, and by adding .GeH2 groups using the Germylene tool.
Presentation Surfaces. Feedstock molecules are simple moieties consisting of one or a few atoms that are bonded to an atomically flat surface called the presentation surface. A tool can then be brought up under positional control to a specific atomic site on the presentation surface and bonded to the feedstock molecule, allowing the tool to remove the feedstock molecule from the presentation surface and then carry it away to participate in further mechanosynthetic operations, e.g., to add one or more atoms to a specific site on an atomically precise workpiece.
.CH2 groups may be distributed on a germanium surface, facilitating their subsequent removal by a dehydrogenated silicon or diamond tool or tip, or on a silicon surface, by several means. For example, a partially methylated germanium surface is prepared by thermal adsorption and reaction of CH4 gas on Ge(100) as described by J. Murota, M. Sakuraba, “Atomically controlled processing for high-performance Si-based devices,” Tohoku-Cambridge Forum (Hall in Peterhouse, University of Cambridge, Organizers: M. Koyanagi, W. I. Milne), International Workshop on Nano-Technology, Nano-Materials, Nano-Devices, and Nano-Systems, 11 Jun. 2004; or by ion bombardment of clean Ge(111) at low substrate temperature (<470 K) using low-energy .CH3 ions, a strongly exoergic radical coupling reaction. CVD of diamond and diamond-like carbon or DLC (C:H films) onto Ge substrates without carbide formation using CH4 feedstock gas is well-known. J. Franks, “Preparation and properties of diamondlike carbon films,” J. Vac. Sci. & Technol. A 7(May 1989):2307-2310; and C. A. Rego, P. W. May, E. C. Williamson, M. N. R. Ashfold, Q. S. Chia, K. N. Rosser, N. M. Everitt, “CVD diamond growth on germanium for infra-red window applications,” Diam. Rel. Mater. 3 (1994):939. (Absorption spectra after hydrocarbon CVD on Ge surfaces indicate that bonding is mainly type sp3 with CH, CH2, and CH3 bonds [O]; a similar experiment on Si substrate found 19.4% sp3 CH3, 23.4% sp3 CH2, and 45.6% sp3 CH species by observing C—H stretch absorption bands. D. S. Patil, K. Ramachandran, N. Venkatramani, M. Pandey, R. d'Cunha, “Microwave plasma deposition of diamond-like carbon coatings,” Pramana J. Phys. 55(November/December 2000):933-939.) Related techniques such as physical vapor deposition (PVD), laser CVD, direct ion beam deposition, dual ion beam sputtering, RF/DC glow discharge or microwave discharge may also be employed. The dissociation of trimethylphosphine (see Y. Fukuda, M. Shimomura, G. Kaneda, N. Sanada, V. G. Zavodinsky, I. A. Kuyanov, E. N. Chukurov, “Scanning tunneling microscopy, high-resolution electron energy loss spectroscopy, and theoretical studies of trimethylphosphine (TMP) on a Si(111)-(7×7) surface,” Surf. Sci. 442 (1999):507-516) on Si(111) and trimethylgallium (see M. J. Bronikowski, R. J. Hamers, “Adsorption and Dissociation of Trimethylgallium on Si(001): An Atomically Resolved STM Study,” Surf. Sci. 348(10 Mar. 1996):311-324) on Si(100) via thermal annealing at 400-500 K leaves isolated .CH2 groups on these surfaces. A CH3-decorated Ge surface may also be prepared via conventional solution-phase chemical methylation since methylated germanium is found in the natural environment; each CH3 is converted to .CH2 using a proto-HAbst or an HAbst tool. C2 (see D. M. Gruen, S. Liu, A. R. Krauss, X. Pan, “Buckyball microwave plasmas: Fragmentation and diamond-film growth,” J. Appl. Phys. 75 (1994):1758-1763), C2H2 (see Ansoon Kim, Jae Yeol Maeng, Jun Young Lee, Sehun Kim, “Adsorption configuration and thermal chemistry of acetylene on the Ge(100) surface,” J. Chem. Phys. 117(8 Dec. 2002):10215-10222), and .GeH2 (see Guangquan Lu, John E. Crowell, “The adsorption and thermal decomposition of digermane on Ge(111),” J. Chem. Phys. 98(15 Feb. 1993):3415-3421) groups can also be distributed on flat silicon or germanium surfaces, providing a convenient presentation surface for carbon dimer and germanium feedstock molecules.
Bootstrapping. Once the first atomically precise tools exist, they can be used to fabricate more of the self-same tools. But the first set of atomically precise tools must be manufactured using only currently available atomically imprecise tools, or proto-tools, a process called bootstrapping. Numerous approaches exist for bootstrapping the first tools from proto-tools, but several examples can be given here. One approach is to synthesize appropriate molecules and then attach these (or similar molecules that have appropriate tooltip structure) to the tip structure of an SPM-like device to create the first proto-tools via tip functionalization; a wide range of molecular structures having the desired functionality similar to atomically precise tools are feasible. Another approach using commercially available SPM ultrasharp tips is disclosed in the detailed description below. Commercially available tips have been used to scan short poly(dG)-poly(dC) DNA fragments deposited on modified HOPG (highly oriented pyrolytic graphite), enabling detection of single-stranded regions in double-stranded poly(dG)-poly(dC) and double-stranded and single-stranded regions in poly(dG)-poly(dG)-poly(dC) triplexes, as well as the resolution of the helical pitch of the triplex molecules. SPM instruments can already achieve the requisite sub-Angstrom positioning accuracy needed for reliable site-specific atomically precise mechanosynthesis operations.